The present invention relates to piezoelectric devices and, more particularly, to a piezoelectric device which is well suited for interconnecting with other components and which is well insulated. Piezoelectric materials are materials capable of converting electrical energy into mechanical energy and vice versa. Such materials can be used as sensors (mechanical input, electrical output), as actuators (electrical input, mechanical output) or as vibration control devices (active where power is supplied to the system and passive where the energy generated is dissipated by an electrical component). The piezoelectric material may be in plate form (piezoceramic such as PZT 5A or PZT 5H), in fiber form, or as a single crystal. The molecular structure of the piezoelectric material is in crystal form, with the piezoelectric effect occurring along the center axis of the crystal. Poling is the operation performed to align all the piezoelectric crystals in one direction. The direction of alignment is typically referred as the poling direction in which one side of the material has a negative charge, and the opposite side has a positive charge. The maximum efficiency of energy conversion occurs along the poling direction. This is important to know so that there is a direct correlation between the voltage applied and the direction of the motion caused by the piezoelectric material. Piezoelectric materials are typically driven in a “d31” direction (through the thickness) or in a “d33” direction (along the surface of the material). Piezoelectric materials are typically driven at high voltages (+/−200V or +/−400V). The voltages can be hazardous if contacted by an individual during operation. Packaging and electrical insulation is critical for further utilization of such devices in areas where human contact may be possible.
The present invention comprises a novel way to package and manufacture a piezoelectric device. The key features of the packaging method include the encapsulation of the conductive piezoelectric material and the ease of electrical connectivity of the device to an external electrical component. The present manufacturing process employs 1) a lamination process and 2) a coating process. The lamination process is used to adhere one side of the piezoelectric device to a flexible substrate having conductive traces disposed thereon and the coating process is used on the second, opposing side of the piezoelectric device to encapsulate and protect the device. More specifically, the piezoelectric material, in fiber, powder or plate composition, is first bonded to the substrate having the conductive traces via the lamination process. The bonded device is then coated on the exposed side by insulating material that is applied by a spray-paint or powder coating operation. When multiple layers of piezoelectric material are used, copper-clad flexible conductive material is used in a middle layer (between the two pieces of piezoceramic material) and both external sides of the device are coated.
The advantages of the present invention over prior art piezoelectric packaging techniques is the ability to obtain very good energy transfer through the thin copper-clad conductive material, and to provide very good insulation and impact resistance to the outside environment through the coating process. Additionally, the manufacturing process used is straight forward and allows for high volume and low cost manufacture of piezoelectric devices. The use of flex circuitry material makes the electrical connections to the piezoelectric devices very reliable and easy to use.